U.S. patent number 6,116,517 [Application Number 09/214,361] was granted by the patent office on 2000-09-12 for droplet mist generator.
This patent grant is currently assigned to Joachim Heinzl. Invention is credited to Ingo Ederer, Josef Grasegger, Joachim Heinzl, Wolfgang Schullerus, Carsten Tille.
United States Patent |
6,116,517 |
Heinzl , et al. |
September 12, 2000 |
Droplet mist generator
Abstract
In a pump chamber connected to a liquid supply, an overlapping
piezoelectric flexural transducer is disposed so that when voltage
pulses are applied to produce an excursion, a number of droplets
can be expelled from a nozzle array in the housing wall of the pump
chamber using a plurality of nozzles. Gaps are formed between the
edges lateral to the direction of overhang an the free end of the
piezoelectric flexural transducer ad adjacent section of the
housing wall. The nozzle array can be disposed in the projection of
the plate surface of the piezoelectric flexural transducer in its
direction of motion or in the extension of the piezoelectric
flexural element or in another suitable pattern. As part of a
combustion device the droplet mist generator is excellent for
producing a combustible fuel-oxidant mixture.
Inventors: |
Heinzl; Joachim (Munchen,
DE), Ederer; Ingo (Munchen, DE), Grasegger;
Josef (Garmisch-Partenkirchen, DE), Schullerus;
Wolfgang (Bad Feilnbach, DE), Tille; Carsten
(Munchen, DE) |
Assignee: |
Joachim Heinzl (Munich,
DE)
|
Family
ID: |
7798598 |
Appl.
No.: |
09/214,361 |
Filed: |
May 11, 1999 |
PCT
Filed: |
June 24, 1997 |
PCT No.: |
PCT/DE97/01307 |
371
Date: |
May 11, 1999 |
102(e)
Date: |
May 11, 1999 |
PCT
Pub. No.: |
WO98/00237 |
PCT
Pub. Date: |
January 08, 1998 |
Foreign Application Priority Data
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|
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Jul 1, 1996 [DE] |
|
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196 26 428 |
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Current U.S.
Class: |
239/101;
417/410.2 |
Current CPC
Class: |
B41J
2/14282 (20130101) |
Current International
Class: |
B05B
17/04 (20060101); B05B 17/06 (20060101); B01F
3/04 (20060101); B41J 2/14 (20060101); B05B
1/02 (20060101); B05B 1/08 (20060101); F04B
43/02 (20060101); F04B 43/04 (20060101); F23D
11/00 (20060101); F23D 11/34 (20060101); H02N
2/00 (20060101); B05B 001/08 () |
Field of
Search: |
;417/410.2
;239/99,101,102.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0337429A |
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Oct 1989 |
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EP |
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0427291A |
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May 1991 |
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EP |
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0516188A |
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Oct 1992 |
|
EP |
|
0612621 |
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Aug 1994 |
|
EP |
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634273A2 |
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Jan 1995 |
|
EP |
|
713773A2 |
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May 1996 |
|
EP |
|
2912620A |
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Oct 1979 |
|
DE |
|
3306101A |
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Aug 1984 |
|
DE |
|
3317082A |
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Nov 1984 |
|
DE |
|
3705980 |
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Sep 1988 |
|
DE |
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19507978A1 |
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Sep 1996 |
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DE |
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61-03357A |
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Jun 1986 |
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JP |
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1-18643 |
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Jan 1989 |
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JP |
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01105746A |
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Jul 1989 |
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JP |
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3-7348A |
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Jan 1991 |
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JP |
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03216344A |
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Dec 1991 |
|
JP |
|
Other References
Siemens, Piezoelektrische Biegewandler, Oct. 1984..
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Primary Examiner: Weldon; Kevin
Attorney, Agent or Firm: J.C. Patents Huang; Jiawei
Claims
What is claimed is:
1. Droplet mist generator for producing a droplet mist
comprising:
a pump chamber connected to a fluid reservoir and bounded by a
casing wall;
a nozzle area constructed in the casing wall, said nozzle area
having a plurality of nozzles;
a plate-shaped, piezoelectric flexural transducer positioned in the
pump chamber and attached so that it forms an overhang and is
bendable around a transverse axis that runs transversely to the
direction of the overhang for alternatingly carrying out a
displacement stroke, wherein fluid is driven towards the nozzles of
the nozzle area and fluid droplets produced are ejected from the
nozzles in the form of a droplet mist and a return stroke, whereby
the piezoelectric flexural transducer is common to the plurality of
the nozzles of the nozzle area;
side openings formed between lateral edges of the piezoelectric
flexural transducer and a portion of the casing wall lying opposite
to said lateral edges, and wherein a connection between the fluid
reservoir and the pump chamber empties into the pump chamber at the
side of the piezoelectric flexural transducer turned away from the
nozzle area, and;
a control system by which the piezoelectric flexural transducer is
controlled by voltage pulses for the displacement stroke, which
occurs more quickly than the return stroke in which the fluid flows
back through the side openings.
2. Droplet mist generator according to claim 1, whereby the pump
chamber is connected to the fluid reservoir through several
lines.
3. Droplet mist generator according to claim 1, whereby the
connection between the pump chamber and the fluid reservoir has a
choke site.
4. Droplet mist generator according to claim 1, whereby the nozzles
are designed to taper in the direction away from the pump
chamber.
5. Droplet mist generator according to claim 1, whereby that part
of the casing wall constructed with the nozzle area is covered on
outside with Teflon.
6. Droplet mist generator according to claim 1, whereby the
piezoelectric flexural transducer is a multi-layer piezoelectric
ceramic transducer with an additional passive piezoelectric ceramic
layer.
7. Droplet mist generator according to claim 1, whereby the nozzle
area is constructed in a first part of the casing wall that is
located under the overhang of the piezoelectric flexural transducer
in the direction in which a free end of the piezoelectric flexural
transducer can be moved, and a frontal gap is constructed between
the free end of the piezoelectric flexural transducer and a second
part of the casing wall lying opposite to said free end.
8. Droplet mist generator according to claim 7, whereby in an
equilibrium position of the piezoelectric flexural transducer,
which occurs when the voltage is not on, an equilibrium gap is
formed between the piezoelectric flexural transducer and that part
of the casing wall where the nozzle area is constructed, and by
applying the voltage, the piezoelectric flexural transducer can be
moved to or from the nozzle area.
9. Droplet mist generator according to claim 8, whereby the frontal
gap constructed between the free end of the piezoelectric flexural
transducer and the second part of the casing wall lying opposite to
said free end is not more than five times as large as the
equilibrium gap.
10. Droplet mist generator according to claim 9, whereby in the
equilibrium position of the piezoelectric flexural transducer,
which occurs when the voltage is off, the piezoelectric flexural
transducer contacts that part of the casing wall where the nozzle
area is constructed, and the piezoelectric flexural transducer can
be moved away from the nozzle area by applying voltage.
11. Droplet mist generator according to claim 7, whereby that part
of the casing wall where the nozzle area is constructed projects
into the pump chamber.
12. Droplet mist generator according to claim 7, whereby an
arrangement that is essentially mirror-inverted to the
piezoelectric flexural transducer and the nozzle area and that has
a second piezoelectric flexural transducer and a second nozzle area
is positioned opposite to the free end of the piezoelectric
flexural transducer, and the control system is constructed so as to
control the piezoelectric flexural transducer and the second
piezoelectric flexural transducer with varying pulse frequencies,
pulse lengths, and/or pulse phases.
13. Droplet mist generator according to claim 1, whereby the nozzle
area is positioned in that part of the casing wall opposite to a
free end of the piezoelectric flexural transducer.
14. Droplet mist generator according to claim 1, wherein the
droplet mist generator is coupled to a burner as a component of the
burner, whereby the fluid reservoir is a fluid fuel reservoir, and
the nozzles of the nozzle area serve as burner nozzles and have a
smallest diameter of at least 10 .mu.m and at most 100 .mu.m.
15. Droplet mist generator according to claim 14, whereby a
distance between mid-points of neighboring nozzles of the nozzle
area serving as the burner nozzle is at least 50 .mu.m and at most
2,000 .mu.m.
16. Droplet mist generator according to claim 1, which has at least
50 said nozzles.
Description
This application is a 35 U.S.C. 371 of application number
PCT/DE97/010307 filed Jun. 24, 1997.
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention concerns a droplet mist generator and, in particular,
a droplet mist generator as apart of a burner.
2. Summary of the Invention
Micro-droplet mist generators for producing individual droplets on
call are known in ink printing. In EP-O 713 773 a droplet mist
generator with piezoelectric flexural transducers and a nozzle each
under the transducer is proposed in which the individual
transducers with partition walls are separated from each other so
that when the transducer is deflected from the true path, a droplet
is ejected from the nozzle assigned to another transducer.
From the older German patent application with the file number
19507978.7 a dosing system for fuel dosing is known that has
numerous micro-nozzles and electrothermic, electrostatic,
electrodynamic, or piezoelectric transducers with which an
expansion of vapor bubbles in a fuel-filled chamber or a change in
volume of this chamber is effected by means of an electrical
trigger signal, therefore making it suitable for the repeated
ejection of fuel droplets that are essentially of the same size.
The use of a piezoelectric membrane actuator is described as a
preferred transducer principle.
When using the expansion of vapor bubbles as an actuator principle
for dosing traditional types of fuel, the various components of the
fuel vaporize under very different conditions. The vaporization
therefore does not occur abruptly enough to achieve an efficient
formation of droplets. Variations in the composition of the fuel
lead, in addition, to irregularities so that reliable dosing or
transport is not possible when using the vapor bubbles principle.
Transducers in which the chamber volume is changed are complicated
structures. In the case of a piezoelectric flexural transducer, for
example, a piezoelectric ceramic element is covered with a membrane
that forms a chamber wall. This is necessary to obtain the change
in volume, because when a piezoelectric crystal expands in a
direction, there is always a vertical contraction connected with
it. In the piezoelectric flexural transducer and the membrane,
material must be deformed during a large-scale deflection from the
true path so that
works of deformation must be carried out against strong inner
mechanical resistance. Such transducers therefore work with a poor
degree of effectiveness. And in relation to the structural size of
the transducer elements, only a small dispersion is attained due to
the resistance. A high acceleration of fluid also cannot be
obtained.
By using the invention, the problem of creating an inexpensive pump
with a small structural size in which a stream of fluid in the form
of a cloud of droplets can be dosed with a high flow rate while
maintaining a certain droplet size and density is solved.
The problem is solved according to the invention by a droplet mist
generator. The droplet mist generator comprises a pump chamber,
which is constructed in a casing and is connected to a fluid
reservoir; a nozzle area constructed in the casing wall, having a
plurality of nozzles; a plate-shaped piezoelectric flexural
transducer that is positioned in the pump chamber and attached so
that it overhangs and can be bent around a quadrature axis running
transversely to the direction of the overhang; openings that are
constructed between the edges of the piezoelectric flexural
transducer, which form ends in the direction of its quadrature
axis, and the casing wall; and a control system through which
voltage impulses can be applied to the piezoelectric flexural
transducer by bending the piezoelectric flexural transducer,
driving out fluids, and ejecting droplets from the nozzles of the
nozzle area.
With the idea of impacting an entire area of nozzles with a
piezoelectric flexural transducer positioned so it is effectively
fluidic inside a chamber filled with fluid, a droplet mist
generator with an especially high flow rate is created, whereby the
droplet size and density can be determined with the form of the
nozzle area and by means of the length, strength, and frequency of
the pulse emitted by the control system.
Piezoelectric flexural transducers produce an especially high
deflection from the true path when accelerating quickly and can be
operated with high frequencies. In addition, they have only a small
inner mechanical resistance. Using the piezoelectric flexural
transducer principle, a high conversion rate of electrical to
mechanical energy can be obtained with respect to the structural
size. Moreover, piezoelectric flexural transducers are simple
constructions and thus are inexpensive and reliable.
The special arrangement of the transducer and the numerous nozzles
leads to the fact that the transformed mechanical energy can be
used for the production and transport of the droplet stream with a
high degree of efficiency. By transforming the energy directly near
the nozzles on which the droplets are formed, a high share of
fluidic energy is supplied for the formation of droplets and their
transport.
The fluidic losses due to the compression of the fluid are,
moreover, minimized because the transformer surface, in front of
which a peak pressure is produced during the impacting action, with
the nozzle areas faces a large nozzle cross-sectional area, through
which a conversion of the produced pressure takes place during
transport by forming and ejecting droplets. In other words, a large
share of the generated pressure is transformed.
Through the high acceleration of the piezoelectric flexural
transducer the entire energy is supplied to the droplets forming on
the nozzle in the shortest time span, which leads to an abrupt
breaking off of the droplets while preventing a larger back-flow
into the chamber.
The opening between the edges of the piezoelectric flexural
transducer and the casing wall allows the fluid to stream around
the piezoelectric flexural transducer during the backward movement
of the piezoelectric flexural transducer so that the increasing
volumes between the piezoelectric flexural transducer and the
nozzle area are filled with the fluid that is flowing back and no
air is pulled into the nozzles in the chamber. The openings are
therefore calculated to be so large that fluidic resistance that
occurs due to friction remains small enough that the deflection
from the true path is not greatly impaired. At the same time, the
openings are calculated so they are so small that during the rapid
impacting action of the piezoelectric flexural transducer the fluid
located in front of the transducer cannot be carried off quickly
enough through the opening and is pushed through the nozzles.
The voltage pulses given off by the control system are coordinated
in such a way that the transport of fluid is made possible. The
impacting action, which causes the ejection of droplets through the
nozzle, can occur considerably more quickly than the backward
movement of the piezoelectric flexural transducer so that during
the impacting action no streaming occurs through the opening in
which the backward flow runs against a sufficiently strong stream.
For the purposes of the present invention, a known control system
can be used.
By using a single piezoelectric flexural transducer to impact
several nozzles, the system is inexpensive and not very prone to
problems.
According to the invention the chamber and fluid reserve can be
connected to any suitable place in the chamber. Preferred, however,
is a connecting line on one of the sides of the piezoelectric
flexural transducer turned away from the nozzle area. If one does
not completely reduce the volume of the chamber, but reduces the
volume between the piezoelectric flexural transducer and the
nozzles, when the volume on the opposite side is raised, fluid can
be drawn from the fluid reserve connected to the pump chamber while
the droplets are ejected. In so doing one can obtain especially
short repeat times between the successive surges or bending and
droplet-ejection operations, as a result of which the transport
performance is raised even more.
According to the invention the chamber can be connected to the
fluid reserve by means of a line or other connection. Preferably,
however, the chamber is connected to the fluid reserve through
several lines, especially two lines. In so doing, the droplet mist
generator can be degassed during operation by providing fluid
through a connecting line and carrying away gas and fluid through
the other connection lines. Moreover, an improved and quicker fluid
feed can be obtained with a majority of lines, each in a suitable
arrangement, which leads to a shortened refill time between two
droplet-producing pulses.
According to the invention the connections between the chamber and
fluid reserve can be designed so there is as little resistance as
possible. Preferred are, however, choke sites in the connections
that provide that the least possible fluid is driven through the
feed lines that connect the chamber with the fluid reserve, thus
guaranteeing that the transport performance of the droplet mist
generator is high. Preferably the choke sites are designed in such
a way that the fluid goes against a high fluidic resistance during
a high pressure impulse when a droplet is ejected, while with a
small difference in pressure during the refill operation the fluid
goes against only a small fluidic resistance and thus the spray
frequency can be increased. Flap valves can also be provided in the
connections so that a streaming of fluid into the chamber through
the connection is made possible while at the same time preventing
the fluid from streaming out.
According to the invention the nozzles can be designed as
cylinder-shaped channels, openings, channels with square
cross-sectional areas, or channels of any other shape; and they can
have a constant channel cross section. They can also be designed so
they taper toward the chamber. It is, however, preferable that they
are designed so they taper in the direction away from the chamber.
In so doing, the cross-sectional area of the nozzle with the
smallest diameter is obtained on the opening of the nozzles in the
surrounding environment. Because bordering surfaces between two
fluids constantly strive to take on the state with the least energy
in the smallest area of the boundary surface, a nozzle tapering
outward leads to a situation in which the edge of the meniscus
between the fluid and gaseous environment constantly strives to
remain on the outer edge of the nozzle. By reducing the extent of
the change in the position of the meniscus edge, the droplet mist
generator is guaranteed to work in an especially robust way, which
leads to a higher transport performance because no outfall cycles
result.
According to the invention, the outer side of the casing wall in
the part of the casing wall in which the nozzle field is positioned
can be made of any suitable material. Preferred, however, is a
coating with teflon or with another suitable anti-adhesive
material. With such a coating one prevents the outer side from
being moistened, i.e., a moving forward of the 3-phase boundary
between fluid, gaseous surroundings and the casing structure
results from opening the nozzle. As a consequence, the meniscus
edge remains at the end of the nozzle toward the outside during the
formation of the droplets, as a result of which the invention is
guaranteed to work in a robust fashion with a high transport
performance.
According to the invention the droplet mist generator can have any
suitable piezoelectric flexural transducer. Preferably, however,
the piezoelectric flexural transducer is a multiple-layer
piezoelectric ceramic transducer with an additional passive
piezoelectric layer. In so doing, the same deflection of the
piezoelectric flexural transducer can be obtained with a small
control voltage. This has the advantage that the regulations for
the maximum voltage can be observed with many possible uses of the
droplet mist generator without limiting the productivity.
According to the invention the droplet mist generator can have only
one piezoelectric flexural transducer and only one nozzle area.
According to the invention a majority of piezoelectric flexural
converters and/or a majority of nozzle areas can be provided in the
droplet mist generator. In this connection several piezoelectric
flexural transducers are arranged in such a way that their plate
surfaces can be positioned in a plane next to one another or their
plate surfaces can be positioned in various levels so they overlap
each other or are positioned next to each other. In a preferred
form of the model an arrangement is provided with a second
piezoelectric flexural transducer and a second nozzle area that lie
across from the free end of the first piezoelectric flexural
transducer and that are essentially mirror-inverted to the first
piezoelectric flexural transducer and the first nozzle area. The
control system in this case is constructed in such a way that the
piezoelectric flexural transducer and the second piezoelectric
flexural transducer can be controlled by various pulse frequencies,
pulse length, and/or pulse phases. The arrangement of the two
piezoelectric flexural transducers lying across from one another
with the same control of the piezoelectric flexural transducers
leads to a situation in which the fluid, which is driven out to the
other piezoelectric flexural transducer, is subject to fluidic
resistance due to the incoming fluid forced out of the other
piezoelectric flexural transducer. As a result, a higher pressure
can build up and the transport flow rate can be increased. By using
a control with shifted pulse phase the transport flow rate can be
varied. A control can also be carried out with various pulse
frequencies and/or pulse lengths. A variation or different control
with respect to one or more of the parameters pulse frequency,
pulse length, and pulse phase can also be used with a set nozzle
arrangement in the nozzle area to vary the droplet size and droplet
speed.
According to the invention the nozzle area can be designed in any
suitable part of the casing wall. In an especially preferred form
the nozzle area is designed in a part of the casing wall that is
positioned inside the overhang of the plate surface of the
piezoelectric flexural transducer in the direction in which the
free end of the piezoelectric flexural transducer is movable when
passing through its equilibrium position. The nozzles of the nozzle
area are thus essentially positioned in such a way that all the
nozzles would be covered by the transducer surface if one would
move the piezoelectric flexural transducer up to the part of the
casing wall in which the nozzles are constructed. In this working
model an opening of a suitable size is designed between the free
end of the piezoelectric flexural transducer and the part of the
casing wall lying across from it in the extension of the
transducer.
According to the invention any suitable distance or no distance at
all may separate the piezoelectric flexural transducer from the
part of the casing wall in which the nozzle area is designed. In a
preferred form of the model when the piezoelectric flexural
transducer is in its equilibrium position, a small distance between
the piezoelectric flexural transducer and the part of the casing
wall in which the nozzle area is designed is formed. In this case
the piezoelectric flexural transducer can be moved away from the
nozzle area by applying a voltage pulse and then moved back to the
nozzle area by applying a reverse polarized voltage or using
mechanical restoring forces, whereby the droplet ejection is
effected. If the distance is chosen to be small enough,
overshooting the equilibrium position when moving it back can lead
to a situation in which the piezoelectric flexural transducer hits
against the casing wall in which the nozzle area is constructed.
The piezoelectric flexural element can, however, be moved away by
applying the voltage pulse immediately in the direction toward the
nozzle area so that the droplet ejection can be started directly
when applying the voltage pulse. In this case as well the
piezoelectric element hits against the casing wall. This bumping
against the casing wall can have the advantageous effect that the
acceleration of fluid is quite abruptly broken off, resulting in an
especially regular and quick break off of the droplets. How strong
this effect is can depend upon how the piezoelectric flexural
transducer and the part of the casing wall in which the nozzle area
is constructed are formed. If there are plane surfaces, contact
will occur to a great extent across the entire surface; if there
are arched surfaces or non-plane surfaces shaped in another form,
contact occurs only at one or a few places.
The opening between the free end of the piezoelectric flexural
transformer and the casing wall lying opposite it in the extension
of the piezoelectric flexural transformer can have any width
according to the invention. Preferably, however, it is not more
than five times as large as the gap that occurs when the
piezoelectric flexural transformer is in equilibrium position when
no voltage is applied.
In another preferred form of the model the piezoelectric flexural
transformer in its equilibrium position, which occurs when no
voltage is applied, lies on the part of the casing wall in which
the nozzle area is constructed and the piezoelectric flexural
transformer is moved away from the nozzle field by applying voltage
by using the control system. In this case the formation of droplets
is triggered when the piezoelectric flexural transducer springs
back after the voltage pulse ends by applying a reverse voltage
impulse or mechanical restoring force.
According to the invention the part of the casing wall in which the
nozzle area is constructed can be constructed like the other parts
of the casing wall. Preferably the part of the casing wall
nonetheless projects into the chamber. Such a form has the
advantage that high pressure, which builds up in the gap that
becomes more and more narrow as the surface of the piezoelectric
flexural transducer is moved to the casing wall, builds up only in
the area in which it falls when the droplets emerge from the
nozzles and thus can be utilized. As a result, there is a reduction
of the fluidic losses during the droplet ejection operation and
thus an increase of the transport performance and the efficiency of
the pump. An advantageous effect is also obtained when the fluid is
refilled from the reservoir. The narrow distance between the
piezoelectric flexural transformer and the casing wall, in which
fluid can only flow against a high fluidic resistance, is shorter
compared to a form of the model without casing wall parts designed
to project into the chamber. As a consequence, the necessary fluid
can be drawn back more quickly and the droplet production frequency
and the transport quantity can be further increased.
In another preferred form of the model the nozzle area is
positioned so it lies across from the free end of the piezoelectric
flexural transformer in the extension of the piezoelectric flexural
transformer. In this way the nozzle area is staggered a little bit
with respect to the free end of the piezoelectric flexural
transformer. The nozzles are thus, preferably, in the direction of
overhang of the piezoelectric flexural transformer. Such an
arrangement has the advantage that it is possible, given an
especially
small construction size, to arrange a majority of the piezoelectric
flexural transformers in the direction of the plate surface one
after the other or inside the plate surface plane next to each
other, whereby each piezoelectric flexural transformer can be
assigned to a corresponding nozzle area without having to further
enlarge the construction area required to set up the piezoelectric
flexural transformer due to the nozzle area. Preferably, in this
arrangement when the piezoelectric flexural transformer is in its
equilibrium position, there is a gap between the piezoelectric
flexural transformer and the next wall lying vertical to the plate
surface of the piezoelectric flexural transformer.
According to the invention the droplet mist generator is a droplet
mist generator for any suitable fluids. In this connection the
droplet mist generator according to the invention can be used
separately or as a component of any suitable system. Preferably,
the droplet mist generator is nonetheless a component of a burner,
whereby the fluid reserve is a fluid fuel reserve. The nozzles of
the nozzle area serving as burner nozzles have a smallest diameter
of at least 10 .mu.m and at most 100 .mu.m. As a result, droplet
sizes are obtained that are especially well-suited for the
production of an inflammable mixture made of fuel droplets and a
gaseous oxidant. With traditional fluid fuels such as diesel fuel
or gasoline, such droplet sizes lead to a situation in which the
fuel droplets completely evaporate right after the ejection from
the nozzle, resulting in an inflammable and/or highly combustible
mixture. Depending on the viscosity and transport quantity, the
nozzles according to the invention have diameters larger than 100
.mu.m corresponding to the fluidic requirements.
According to the invention the mid-points of each of the
neighboring nozzles of the nozzle area that serve as burner nozzles
have any suitable distance between them. Preferably, the mid-points
nonetheless occur at intervals of at least 50 .mu.m and at most
2,000 .mu.m. By choosing the distances between the neighboring
nozzles in this arrangement one obtains a further improvement of
the fuel-oxidant mixture, and with it a further increase in the
burner performance.
According to the invention the droplet mist generator can have any
number of nozzles depending on its use. Preferably, however, the
droplet mist generator has at least 50 nozzles. With at least 50
nozzles or more a burner is especially well suited for use as a
burner for vehicle heating or household heating devices.
In another preferred form of the model holes are provided in the
piezoelectric flexural transducer according to the invention to
reduce the fluidic resistance of the piezoelectric flexural
transducer. In yet other forms of the model valves according to the
invention can be provided in the droplet mist generator with which
the transport of fluid is possible even with larger nozzle
diameters. In this connection the invention provides that either
droplets or a continuous stream of fluid is transported.
Preferably, the operation of existing valves is carried out with a
piezoelectric flexural transducer that simultaneously converts the
fluidic energy. According to the invention the chamber on the
nozzles can also be sealed off against its surroundings by bringing
the piezoelectric flexural transducer into a certain position.
BRIEF DESCRIPTION OF THE DRAWINGS
Advantageous forms of the invention are described in connection
with the drawing. The following are shown in the drawings.
FIG. 1a shows a sectional view transverse to the direction of
overhang of the piezoelectric flexural transducer of a droplet mist
generator in accordance with a working form of the invention,
whereby the piezoelectric flexural transducer is in its equilibrium
position.
FIG. 1b is a sectional view of the droplet mist generator in
accordance with FIG. 1a, whereby the piezoelectric flexural
transducer is deflected by applied voltage.
FIG. 1c is a sectional view of the droplet mist generator from FIG.
1a along the dotted line drawn in in FIG. 1b.
FIG. 2a is a sectional view of a droplet mist generator according
to another model of the invention in which the part of the casing
wall in which the nozzle area is constructed projects into the
chamber, whereby the piezoelectric flexural transducer is in its
equilibrium position.
FIG. 2b is a sectional view of the droplet mist generator according
to FIG. 2a, whereby the piezoelectric flexural transducer is
deflected by applied voltage.
FIGS. 3, 4, and 5 are all sectional views of a droplet mist
generator in accordance with another working form of the model.
FIG. 6 is a sectional view of a droplet mist generator in
accordance with yet another working form of the model in which two
arrangements from a piezoelectric flexural transducer and a nozzle
area face each other in mirror-inverted fashion with respect to the
free end of the piezoelectric flexural transducer.
FIG. 7 is a sectional view of a droplet mist generator in
accordance with yet another working form of the model in which the
nozzle area is positioned opposite its free end lying in the
extension of the piezoelectric flexural transducer.
FIGS. 8, 9, 10, 11, 12 are all sectional views of a droplet mist
generator in accordance with yet another working form of the model
in which the nozzle area is positioned opposite the free end lying
in the extension of the piezoelectric flexural transducer.
FIG. 13a is a sectional view of a nozzle area designed according to
the invention.
FIG. 13b is a top view onto the nozzle area designed according to
the invention and represented in FIG. 13a.
FIG. 14 is a view of a droplet mist generator from FIG. 9 in a top
view in the direction vertical to the plate surface of the
piezoelectric flexural element.
FIG. 15 is a representation of an example of the contact of a
piezoelectric flexural transducer in a droplet mist generator
designed according to the invention.
FIG. 16 is a principal representation of a bimorph piezoelectric
flexural transducer.
FIG. 17 is a principal representation of a monomorph piezoelectric
flexural transducer.
FIG. 18 is a principal representation of a multi-layer
piezoelectric flexural transducer.
And FIG. 19 is a principal representation of a control system used
in accordance with a working form of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In FIGS. 1a to 1c one can see a construction of a droplet mist
generator according to an advantageous working form of the
invention. In a casing a pump chamber 1 is constructed that can be
filled with fluids. The casing wall 2 is formed by a casing base
part 2c, a casing middle part 2b, and a casing top part 2d. Inside
the chamber 1 a piezoelectric flexural transducer 4, which can be
deflected from its true path by the control system 6 (not shown in
FIGS. 1a-1c), is attached so it overhangs. As can be seen in FIGS.
1a and 1c, the piezoelectric flexural transducer 4 is designed in a
plate shape. Its end 4e is attached inside the casing. The opposite
end 4d is free. The plate surface 4c is bounded by the edges 4b
positioned on the sides in the direction of the overhang. The
piezoelectric flexural transducer 4 is made of two layers 4f, 4g of
piezoelectric ceramic. By applying voltage, the piezoelectric
flexural transducer 4 can be bent around the axis 4a running
transverse to the direction of overhang. With such bending, as can
be seen in FIG. 1b, the free end 4d moves along a curve, which, by
way of approximation, corresponds to a movement vertical to the
direction of overhang and to the neutral axis 4a.
A part 2a of the casing wall 2 is positioned inside the overhang of
the plate 4c on the casing wall 2 in the direction of the movement
of the free end 4d of the piezoelectric flexural transducer 4 when
it passes through its equilibrium position on the neighboring part
of the casing wall. A nozzle area 3 with a majority of nozzles 3a
is constructed in the part 2a of the casing wall 2. In the working
example shown here the plate surface 4c and the part 2a of the
casing wall 2 are even surfaces that run parallel to each
other.
As can be seen in FIG. 1a, when the piezoelectric flexural
transducer 4, is in equilibrium position, which occurs when the
voltage is off, a gap 7 forms between the piezoelectric flexural
transducer 4 and the part 2a of the casing wall 2 in which the
nozzle area 3 is formed.
As one can see in FIG. 1c, between the edges 4b of the
piezoelectric flexural transducer 4 and the casing wall 2 openings
5a are provided that are dimensioned large enough so that a
movement of the piezoelectric flexural transducer 4 is not opposed
by a flow resistance that is too strong, and when the piezoelectric
flexural transducer 4 is moved back from the nozzle area 3 a
sufficient current linkage can occur so that no air is drawn into
the chamber 1 through the nozzles 3a. At the same time the openings
5a are sufficiently narrow so that when moving the piezoelectric
flexural transducer 4 onto the nozzles 3a the fluid cannot go
around the openings 5a quickly enough but instead is forced through
the nozzles 3a.
Between the free end 4d of the piezoelectric flexural transducer
and the opposite part of the casing wall lying in its extension an
opening 5b is also constructed that is less than 5 times as
wide--namely, about 4 times as wide--as the gap 7. In the working
example seen in FIG. 1 the piezoelectric flexural transducer has
measurements of 9.times.4.times.0.5 mm. The active, free length is
5.5 mm. The deflections that can be obtained on the free end are 25
.mu.m at 50 V.
As one can see in FIG. 1, the chamber 1 on the side of the
piezoelectric flexural transducer 4 turned away from the nozzle
area 3 is built larger than it is on the other side of the gap 7.
When deflecting the piezoelectric flexural transducer 4 from its
true path, excessively large changes in pressure do not occur in
this part of the chamber 1. The casing middle part 2b of the casing
wall 2, which is positioned between the casing base part 2c and the
casing top part 2d and which determines the height of the chamber,
has a height of 675 .mu.m in this example. Preferably, the casing
components are made of silicon.
As is also clear from FIG. 1, the chamber 1 is connected through
lines 8 to a fluid reserve (not shown). Choke sites 8a are
constructed in the lines 8. The lines 8 are at a considerable
distance from each other. They can therefore also be used for
rinsing during the operation of the pump. In this connection it is
advantageous that one of the two lines 8 is positioned at the end
of the casing in the direction toward the free end 4d of the
piezoelectric flexural transducer 4. With a corresponding
orientation of the chamber 1 relative to gravity, the pump can be
degassed by having the fluid flow through the line 8 positioned
centrally, with the outlet through the line 8 positioned at the
end. Gas bubbles that appear rise to the top and are rinsed out of
the chamber 1. When the pump is in operation, the arrangement shown
in FIG. 1, which has several lines 8 that connect the chamber 1 to
the fluid reserve, is also advantageous. In the suction phase,
evenly occurring drops in pressure occur by way of the chamber 1.
The refill operation can thus be completed more quickly when two
lines 8 exist. In the working example shown in FIG. 1 the line 8
has an inner diameter of 1 mm.
By applying voltage impulses to the piezoelectric flexural
transducer 4 by using a control system 6, the piezoelectric
flexural transducer is deflected from its true course. In so doing,
fluid can be driven onto the nozzles and droplets ejected out the
nozzles 3a. In the working form described the piezoelectric
flexural transducer 4 can be moved to and from the nozzle area 3 by
applying voltage my means of the control system 6. As can be seen
in FIG. 1b, the piezoelectric flexural transducer 4 can be
deflected so far by moving it from the nozzle area 3 that the free
end 4d of the piezoelectric flexural transducer 4 hits against the
part 2a of the casing wall in which the nozzle area 3 is
constructed. As a result, the movement of the piezoelectric
flexural transducer 4 is abruptly slowed, which leads to a
particularly advantageous breaking off of the droplets. To improve
the droplet ejection behavior the piezoelectric flexural transducer
4 can, nonetheless, first be moved a certain distance away from the
nozzle area 3 so that a greater amount of fluid exists between the
piezoelectric flexural transducer 4 and the nozzle area 3 before
the piezoelectric flexural transducer 4 is moved onto the nozzle
area 3.
As one can see in FIG. 1, the piezoelectric flexural element
consists of two layers 4f, 4g. They are connected to each other so
they cannot be slid back and forth. From FIG. 17 one can see more
clearly the construction of the piezoelectric element used in this
working form of the invention. It is a monomorph actuator. One of
the layers is made of a piezoelectric ceramic layer; the other, of
metal or another suitable material. Due to the piezoelectric
effect, the piezoelectric ceramic layer is extended or compressed
by applying voltage. When extending or compressing the layer with
respect to the other layer, the layer construction is bent. This
process can be reversed by discharging. This can take place either
by applying the corresponding countervoltage or by a slow,
independent discharging process.
Other working forms of the piezoelectric flexural transducer
according to the invention can be seen in FIG. 16 with a bimorph
piezoelectric actuator and in FIG. 18 with a multi-layer
piezoelectric flexural actuator. In the bimorph actuators two
piezoelectric ceramic plates are provided with an electrode in the
middle, as a result of which both layers are reverse polarized. By
applying voltage the one layer is extended and the other compressed
so that a larger bending occurs with equally applied differences in
voltage. In a multi-layer piezoelectric flexural element the
extensible or compressible layer is constructed from alternately
very thin--e.g., 20 .mu.m--piezoelectric layers and electrodes
stacked on each other, which are fused with each other or firmly
glued together. In this case the electrodes are interlocked as in a
film capacitor--i.e., the inverse polarized electrodes alternate.
As a result the same electrical field strength is produced in the
piezoelectric ceramic layers with low voltage and thus the same
extent of the piezoelectric effect is produced. The operating
voltage falls considerably in such a case, e.g., from several 100 V
to about 30 to 60 V.
As can be seen in FIG. 1, at least two nozzles 3a exist, which form
the nozzle area 3.
In the FIGS. 13a and 13b one can see how the nozzles 3a and the
nozzle area 3 are formed in another advantageous working form. As
is clear in FIG. 13a, the nozzles are designed in such a way that
they taper from the chamber inner side to the chamber outer side.
The part 2a of the casing wall in which the nozzles 3a of the
nozzle area are constructed has a 35-.mu.m thick teflon layer on
the outside (not shown in the diagram).
In FIG. 13b the arrangement of the nozzles is shown in FIG. 13a in
a top view. The nozzles are positioned regularly with an equal
distance between neighboring nozzles. In each case the series of
nozzles is positioned so the nozzles are staggered with respect to
a neighboring series of nozzles. This allows for the possibility of
packing the nozzles as closely as possible while taking into
consideration technical manufacturing specifications.
Another advantageous working form of the droplet mist generator
according to the invention can be seen in FIGS. 2a and 2b. The part
2a of the casing wall 2 in which the nozzle area 3 is formed
projects into the chamber 1. The piezoelectric flexural transducer
4 lies in equilibrium position on the part 2a of the casing wall 2
in which the nozzle area 3 is formed. In the area neighboring on
the nozzle area 3 there is a gap 7 between the piezoelectric
flexural transducer 4 and the casing wall 2. While operating the
droplet mist generator the piezoelectric flexural transducer 4 is
first moved from its equilibrium position from the nozzle area and
then moved back onto the nozzle area 3 by either applying a reverse
polarized voltage or mechanical restoring forces.
In FIG. 3 another working form of the droplet mist generator
according to the invention can be seen. The casing is made of the
three components 2d, 2c, and 2e, which form the casing wall 2. In
this connection the casing base part 2c is designed as a plate. The
piezoelectric flexural transducer 4 is squeezed in between the
casing parts 2c and 2d and anchored in this way. In FIG. 15 one can
see the construction of the contact of the piezoelectric flexural
transducer with the contact springs 10a, 10b in this working
example.
Another working form of a droplet mist generator according to the
invention can be seen in FIG. 4. The casing is made of only two
casing parts, whereby the piezoelectric flexural transducer 4 is
firmly squeezed between the casing base part 2c and the casing top
part 2d lying opposite it.
In FIG. 5 another working form of a droplet mist generator
according to the invention can be seen. As can be seen in the
working form in FIG. 2, the part 2a of the casing wall 2 is formed
so it projects into the chamber 1. In this case the piezoelectric
flexural element 4, however, does not rest on the part 2a of the
casing wall 2 in its equilibrium position; rather, there is a gap
between the piezoelectric flexural transducer 4 and the part 2a of
the casing wall 2. The piezoelectric flexural element can therefore
be bent directly onto the nozzle area so that droplets are ejected
by using the control system 6. If the piezoelectric flexural
element 4 in this working form is then moved away from the nozzle
area 3 by using the control system 6, advantages occur compared to
the working form represented in FIG. 2. The surfaces of the
piezoelectric flexural transducer 4 lying across from each other
and the part 2a of the casing wall 2 are already moistened with
fluid when the piezoelectric flexural transducer 4 is moved away
from the part 2a of the casing wall, as a result of which fluid is
drawn more quickly into the larger-growing gap and a higher spray
frequency is obtained.
Still another advantageous working form of a droplet mist generator
according to the invention can be seen in FIG. 6. Two piezoelectric
flexural transducers 4 and two nozzle areas 3 lie across from each
other in mirror-inverted fashion.
Another advantageous working form of a droplet mist generator
according to the invention can be seen in FIG. 7. The nozzle area 3
in this case is formed in the extension of the piezoelectric
flexural transducer 4 across from the free end 4d of the
piezoelectric flexural transducer in the casing wall. In the
working form that can be seen in FIG. 7 the entire length of the
piezoelectric flexural transducer 4 lies against the casing wall 2,
and the nozzle area 3 is formed in one of the corners of the casing
wall 2 lying across from one of the ends of the piezoelectric
flexural transducer 4. In this case the nozzle area is formed on
the boundary surface between the two casing components--the casing
base part 2c and the casing top part 2d.
In two other advantageous working forms, which can be seen in FIGS.
8 and 9, the entire length of the piezoelectric flexural transducer
4 does not lie against the casing wall 2 in its equilibrium
position; its attached end 4e is anchored onto the casing base part
2c of the casing wall 2, and in the area of the free end 4d of the
piezoelectric flexural transducer 4 there are recesses 9 provided
in the casing base part 2c that are designed as grooves. With the
grooves the space of the chamber 1 is expanded on the side of the
piezoelectric flexural transducer turned away from the lines 8,
through which the chamber 1 is connected to the fluid reserve. The
recesses 9 in the casing base part 2c essentially extend in the
direction of the overhang of the piezoelectric flexural transducer
4. In the corner of the chamber 1 formed in the place of the casing
wall 2 in which the casing base part 2c and the casing top part 2d
meet each other, the recesses 9 change over into the nozzles 3a of
the nozzle area 3. In this corner the recesses 9 form the nozzles
3a in the casing wall alone or together with other partial recesses
in the casing top part 2d, as one can see in FIGS. 8 and 9.
In FIGS. 10, 11, and 12 working forms can be seen in which the pump
chamber 1 and the nozzles 3a are essentially designed as in the
working forms of FIGS. 7, 8, and 9. But the piezoelectric flexural
transducer 4 is not attached to only one casing component part 2c
(as in FIGS. 7, 8, and 9), the piezoelectric flexural transducer 4
is attached to the casing between the casing base part 2c and the
casing top part 2d.
In FIG. 14 in a top view, recesses 9 provided are positioned as in
the working forms of the invention in FIGS. 8, 9, 11, and 12.
An example of a control system 6 in a droplet mist generator
according to the invention can be seen in FIG. 19. As many suitable
known control systems as desired can be used for the purpose of the
present invention.
In an advantageous working form of the invention a frequency
generator is connected at a later point to a MOS-FET circuit, which
interrupts the charging process and thus the deflection process of
the piezoelectric flexural element, which occurs through a power
supply and a resistance, and discharges the piezoelectric ceramic.
In so doing the sudden movement of the piezoelectric flexural
transducer is achieved. In the charging phase, i.e., for example
when moving the piezoelectric flexural transducer 4 away from the
nozzle area 3, the piezoelectric flexural transducer 4 is charged
with a resistance of 270 in about 150 microseconds to 95% of the
power supply voltage. With the rising side of the square wave
signal of the generator at the gate of the MOS-FET the discharging
occurs through the inner resistance of the FETs. This lasts about
100 nanoseconds. Due to the mechanical inertia of the actuator, the
discharging phase must be extended until the piezoelectric flexural
transducer 4 slowed by the fluid completes the movement and the
droplet is ejected. This is achieved with a standard frequency of
5,000 to 6,000 Hz through a pulse-duty factor of 25%, i.e., in a
time of 40 to 50 microseconds.
* * * * *